The invention relates to a drive shaft assembly for transmitting power in a motor vehicle. In particular, the invention relates to a damper insert located in a tubular drive shaft to attenuate vibration and noise.
Drive train systems are widely used for transmitting power from a rotating source to a rotatably driven mechanism. For example, in motor vehicles, an engine/transmission assembly generates rotational power, which is transmitted from an output shaft of the engine/transmission assembly through a drive shaft assembly to an input shaft of an axle assembly that drives the wheels of the vehicle. To accomplish this, a typical drive shaft assembly includes a hollow cylindrical drive shaft tube having a pair of end fittings, such as a pair of tube yokes, secured to the front and rear ends of the tube. The front-end fitting forms a portion of a front universal joint that connects the output shaft of the engine/transmission assembly to the front end of the drive shaft tube. Similarly, the rear end fitting forms a portion of a rear universal joint that connects the rear end of the drive shaft tube to the input shaft of the axle assembly. The front and rear universal joints provide a rotational driving connection from the output shaft of the engine/transmission assembly through the drive shaft tube to the input shaft of the axle assembly.
It is common for a drive shaft assembly to be subjected to vibration from multiple sources while in service. It is desirable to damp such vibrations to reduce noise and vibration in the vehicle. Any mechanical body has a natural resonant frequency, which is an inherent characteristic of the body, its composition, size, and shape. The resonant frequency is comprises many sub-frequencies, often referred to as harmonics. As the rotational speed of a hollow article changes, it may pass through the harmonic components of its resonant frequency. When the rotational velocity of the article passes through these harmonic frequencies, vibration and noise may be amplified because the two frequencies are synchronized, and the rotational energy of the article is undesirably converted into vibration and noise.
A variety of techniques and devices are known for damping the undesirable noise that can be produced by hollow articles during rotation. For example, in a drive shaft assembly, a cylindrical cardboard insert is disposed within a tubular drive shaft to dampen the noise generated during use. In many instances, the outer surface of the cardboard insert is provided with a solid bead of an elastomeric material that extends helically along the length of the tube. The solid helical bead is provided to engage the inner surface of the tube with an elastically developed force to prevent the damper insert from moving relative to the tube in service. As the tube transmits power, it can experience changes in its shape because of torsional and flexural loads. It has been found that engagement of the solid helical bead with the inner surface of the tube causes the insert to change its shape with the hollow article. As a result of this change of shape, the resonant frequency of the cardboard insert changes also, resulting in an undesirable reduction in its ability to dampen noise and vibration.
In addition, the preload force developed in the solid helical bead due to contact with the inner surface of the tube compresses the bead and impairs its ability to deform elastically with the tube. Changes in humidity cause expansion and contraction of the paper insert, which affects the radial space between the damper insert and the inner surface of the tube. The tube itself has variations in its wall thickness and variations in its circularity. These also influence the size of the radial space between the damper insert and the inner surface of the tube.
Although such damper inserts have performed reasonably well in absorbing drive shaft vibrations, they have a tendency to creep relative to the drive shaft due to the repetitive application and release of torsional and flexural displacement. Changes in temperature and humidity cause variations in the ability of the insert to resist vibration-induced deformation of the drive shaft cross section.